Earthbound has four audio effect tables, each representing one SPC700 port.
Note: All addresses in this document are relative to 0x25FB42 in a vanilla ROM.
| Port | Address | Entries | Notes |
|---|---|---|---|
| Port 0 | $180D | 1 | Unused, overridden by music track changes |
| Port 1 | $17D5 | 28 | Used for most music effects |
| Port 2 | $17C5 | 8 | Only used for Giygas static |
| Port 3 | $16C7 | 127 | Used for most sound effects |
Each entry points to an effect, with the byte at offset -1 determining its type.
| Type | Description |
|---|---|
| 00 | Same as 02? Unused? |
| 02 | Single note? [NN HH II VV PP nn TT] |
| 04 | Sequenced [II VV PP TT seq…] |
| 06 | Sequenced, no staccato [II VV PP TT seq…] |
| 08 | Assembly |
| 0A | Like 04, but has a pointer to a second channel at offset -3 |
| 0C | Like 06, but has a pointer to a second channel at offset -3 |
| 0E | Same as 10? Unused? |
| 10 | Noise, single channel. Has a pointer to GAIN data at offset -3 and a pointer to noise clocks at -5 [LL HH II VV PP CC SS] |
| Byte | Description |
|---|---|
| 00 | Terminates sequence |
| 01-7F | Sets note length |
| 80-C7 | Plays a note |
| C8 | Tie |
| C9 | Rest |
| CA | Unknown (noise?) |
| CB-DF | Undefined |
| E0 | Change instrument |
| E1 | Set panning |
| E2-EC | Undefined |
| ED | Set volume |
| EE-FF | Undefined |
???
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